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An international team of scientists has devised artificial silk that becomes a slim yet tough fiber, with help from a machine designed to mimic the spinning spiders do naturally. The silk isn’t quite as strong as the real thing, but the researchers have a few ideas for fine-tuning the technology so it can move a step closer to the market.

Artificial spider silk fibers on spools. (Credit: Marlene Andersson)

Spider-Man jokes aside, spider silk is a natural super-fiber. It’s made from protein, yet it is incredibly stretchy and strong. Pound-for-pound, some fibers of spider silk can absorb more energy than the bulletproof vest material Kevlar. What’s more, spider silk doesn’t provoke immune responses in people, so the fiber has all kinds of medical possibilities, from wound healing patches to artificial tendons. (As an aside, we're talking about a different material from the silk clothing in your closet. That almost certainly came from silkworms raised on a farm, not spiders.)

If spider silk is such big business, why isn’t it everywhere? One obvious-seeming option, farming spiders for their silk, isn’t realistic. Spiders tend to get territorial and eat each other. So scientists have been trying for years to make artificial spider silk instead. New advances make headlines every so often, but by and large making commercial-grade spider silk in labs has proven extremely challenging.

In the last couple of years, though, startups have stepped up to the plate. Japan’s Spiber Inc. has partnered with The North Face to make a synthetic spider silk coat called The Moon Parka (not yet available for sale stateside). San Francisco-based Bolt Threads has announced a deal with Patagonia. Both these companies use single-celled hosts (yeast or E. coli bacteria) to make silk proteins instead of spiders. Other startups are exploring engineered silkworms, and even goats.

So where does this new research fit in? Currently, making spider silk in the lab is a multi-step process. Firms must first make the proteins, then purify them, and finally spin them into fibers. There tend to be a couple of kinks in this process. One is that the proteins clump together, making fewer of them available for spinning. Another is that the spinning process on its own produces relatively weak silk that needs additional processing.

Swedish researchers Anna Rising and Jan Johansson think it’s possible to fix those problems by paying attention to how spiders control their silk-making. They have been publishing work in this area for several years, and are coauthors on patentapplications held by Spiber Technologies AB, a firm in Stockholm. (Spiber Technologies and Japan’s Spiber Inc. are two different companies.) For the current study, Rising and Johansson collaborated with other experts in Europe and China to apply some biochemistry and engineering to the silk-making issues. Their work appears in the journal Nature Chemical Biology.

A nest of artificial spider silk fibers (Credit: Lena Holm)

First, the team reasoned that the silk proteins were clumping because they weren’t dissolving well enough in water at the high concentrations needed to properly spin silk. To solve that problem, they devised a hybrid made with two natural silk proteins from different spiders. Sure enough, the hybrid protein behaved in water even in highly concentrated form.

Second, the researchers wanted to avoid extra processing steps, and they figured mimicking natural spider spinning as much as possible would help. The chemical solvents typically used for artificial spinning, such as methanol, they write, “typically prevent the formation of native-like three dimensional structures,” so they used only water as a solvent. The team developed a machine that pushed the proteins through a tiny glass tip, about half as thick as a human hair, to induce the kind of pressure that occurs in a spider’s silk glands. The machine spat the resulting tiny noodle of protein goop into a container of acidic water, because researchers have learned that acidic pH is an important factor in effective silk fiber formation.

So, does mimicking Mother Nature make a better silk material? The team’s fibers looked and acted almost as good as the real thing. This silk wasn’t as strong as the silk spiders make, but the researchers suspect they’ll get better strength if they can spin narrower fibers, closer to the dimensions spider silk fibers have in nature. On the plus side, the researchers claim their faux spider silk is the strongest yet made without any additional processing.

It’s too soon to tell whether this will be a big improvement in manufacturing artificial spider silk for clothing or medical devices. And whenever you adjust the makeup of a spider silk protein, you're going to want to find out what, precisely, are the advantages of the new fiber over the ones we already have. Still, here’s hoping that the spider silk field in general continues to move forward. As study leader Anna Rising told the New York Timesin 2014: “If we could produce large amounts at a low price, there’s no limit to what it could be used for.”